Electrochemical sensors incorporating diamond-like carbon-coated (DLC-coated) electrodes are
effective tools for online, real-time corrosion monitoring at high temperatures. A vacuum-based
chemical vapor deposition process was used to deposit a DLC thin film coating on the surface of the
sensing electrodes. The chemical inertness of the DLC coating on the sensing electrodes produced a
crevice-free electrode that can be used at temperatures above 100 °C. In this paper, we present the
coating deposition process for sensor electrodes and fabrication of coupled multielectrode array sensors
(CMAS) for high-temperature, high-pressure applications. Probes were fabricated using uncoated and
DLC-coated Alloy 22 (Ni-22Cr-13Mo-3Fe-3W) and Titanium Grade 7 (Ti-0.2Pd) electrodes. The Alloy
22 probes were tested in high-temperature, high-pressure conditions in a pH 10 caustic solution. The
measured non-uniform corrosion rate using the Alloy 22 probe with the DLC-coated electrodes was
approximately 2 µm/yr. The Titanium Grade 7 probes were tested in a dilute NaCl solution saturated
with H2S-CO2 at high pressures in the temperature range of 39-81 °C and in a saturated solution
containing NaCl-NaNO3-KNO3 at 150 oC. The stabilized localized corrosion rates for probes with or
without the DLC coating were less than 1 µm/yr in the H2S-CO2 environment, and less than 0.03 µm/yr
in the NaCl-NaNO3-KNO3 salt mixture at 150 °C. The test results indicate that Titanium Grade 7 is not
subject to crevice corrosion under the testing conditions.
Keywords: Corrosion-resistant coating, multielectrode sensor, corrosion monitoring, high-temperature
corrosion sensor, coupled multielectrode